The present invention relates to a substrate disk comprised of two substrates connected to one another and having a center hole.
Substrate disks of this kind are, for example, known as so-called digital versatile disks (DVD), e.g. video and other data disks, and are comprised of two substrates or partial substrates having digital information stored on a respective surface thereof and connected by gluing the faces to one another. For connecting the two substrates to form a substrate disk, for example, a digital video disk, very precisely operating devices are required because the substrates not only must be positioned precisely one above the other, but also the gluing process must be uniform over the entire substrate surfaces and without inclusion of air bubbles and producing adhesive layers of different thickness. This is necessary in order to provide high-quality fail-safe substrate disks. Furthermore, the conventional devices for gluing the two substrates are very complicated in their construction and require a large space. For the step of gluing, the two substrates must be aligned very precisely relative to one another which is very difficult to achieve. Furthermore, there is the risk that the two substrates forming the substrate disk can accidently separate from one another. For example, when removing a DVD from a DVD player that can accommodate multiple DVDs, it may occur that the DVD to be removed is canted so that the substrates will separate from one another. A further disadvantage of the gluing process is that the adhesive or glue lacquer can enter the center hole since one substrate is pressed onto the other after application of the adhesive in the inner area of the other substrate. This results in changes of the inner diameter of the center hole and diminishes the quality of the substrate disk.
It is therefore an object of the present invention to provide a substrate disk which can be produced with minimal reject rate and which has improved quality and service life.
This object is inventively solved in that one of the substrates forming the substrate disk is provided at the circumference of the center hole with at least one projection projecting from the substrate face. This has the advantage that upon connection, for example, by gluing, of the substrates a precise centering is possible without additional centering measures or devices. During the gluing step of the substrate disk, the adhesive is applied in the vicinity of the center hole onto one of the substrates. The other substrate is then placed thereon and pressed against the first substrate to a greater or lesser degree. In conventional substrate disks the adhesive can reach the center hole during this process so that the dimensional specifications of the disk can no longer be maintained and the quality specifications are no longer met. The projection at the circumference of the center hole of one of the substrates prevents the adhesive from flowing into the center hole. Furthermore, the substrate disk, because of the presence of the projection at the circumference of the center hole of one of the substrates, is protected to a greater extent with respect to accidental separation of the two substrates from one another when the substrates, for example, upon lifting from the receiving pin of the DVD player are canted.
In one advantageous embodiment of the invention the projection of the one substrate extends over the entire circumference of the center hole. This ensures that the adhesive or adhesive lacquer after pressing one substrates on to the other substrate, cannot penetrate at any location of the circumference of the center hole into the circumferential wall surface of the center hole. Furthermore, with the additional gluing of the circumferential wall surface of the center hole an especially stable connection of the two substrates is achieved.
In another advantageous embodiment of the present invention, the other substrate without projection is provided at the inner edge of the center hole with a recess which can be, for example, concave. This recess serves as a reservoir for the adhesive or the adhesive lacquer which will flow, upon pressing of the substrates onto one another, in the direction of the center hole of the substrate disk.
In yet another advantageous embodiment of the invention, the transition portion between the face of the substrate and the projection is slanted or rounded. This allows an easier flow of the plastic material during manufacture of the substrate by a molding process in comparison to a right angle embodiment of the transition portion so that the substrate homogenitity and thus the quality of the substrate disk are improved. Furthermore, such an embodiment reduces the risk of breakage of the projection and thus increases the stability of the substrate disk.